In recent years, computerized construction has come to be introduced to civil engineering using construction machines, and the like. The “computerized construction” refers to a construction process, in which ICT (Information and Communication Technology) and RTK-GNSS (Real Time Kinematic-Global Navigation Satellite Systems) are used in a construction work (e.g. civil engineering) using construction machines such as a hydraulic excavator, a bulldozer and a motor grader to detect the position of a work point of working equipment mounted on the construction machines, so that the working equipment based on the detected work point can be automatically controlled and/or information on a geometry of the construction site and the work point in the geometry can be displayed on a display device in a cab, thereby efficiently performing the construction work (sometimes referred to simply as “work” hereinafter) and obtaining highly accurate construction results.
In such an computerized construction, the work point of the working equipment is, for instance, a blade edge position of a bucket when the construction machine is a hydraulic excavator. The blade edge position is calculated in a coordinates of designed position based on parameter such as a positional relationship between a GNS antenna and a boom foot pin, a length of each of a boom, an arm, and a bucket, and a stroke length of each of a boom cylinder, an arm cylinder, and a bucket cylinder.
However, when the lengths of the boom, the arm, the bucket and the cylinder for each of the boom, the arm and the bucket are designed values, since there are errors between the actual lengths of each of the components and the designed values due to a dimension tolerance for manufacture and assembly processes, the calculated position coordinates and the actual coordinates of the blade edge position are not necessarily the same, so that the accuracy in detecting the blade edge position is reduced. Accordingly, in order to enhance the detection accuracy of the blade edge position, the parameters used for the calculation have to be calibrated using predetermined calibration values based on position coordinates obtained through an actual position measurement, thereby requiring a calibration process (e.g. position measurement).
As an example of such a calibration process, it is known to provide a total station at a position several meters away from a boom foot pin and the position of a measurement point defined near a blade edge of a bucket is measured using the total station (see, for instance, Patent Literature 1). In the calibration process disclosed in Patent Literature 1, the blade edge of the bucket is positioned at a plurality of measurement positions including a ground surface position and a position above the ground surface by a predetermined height, and the position of the measurement point is measured at each of the plurality of measurement positions. Then, the calibration values of the parameters are calculated based on the position coordinates of the plurality of measurement points.
A prism mirror (sometimes referred to simply as a “prism” hereinafter) is attached near a blade edge to measure the blade edge position. Specifically, a laser beam is radiated from the total station to the prism and a light reflected from the prism is measured.